Bladder insert for encapsulant displacement

ABSTRACT

An encapsulated device and method for making such encapsulated device containing a bladder disposed between a wall of the case and the encapsulant. The bladder defines a space devoid of encapsulant and contains a collapsible insert such as an open cell foam material, thereby allowing the unimpeded thermal expansion of the encapsulant. By reducing thermal expansion stresses on the encapsulated devices, the reliability of the encapsulated device is improved.

[0001] This application is a continuation-in-part of co-pending andcommonly assigned U.S. patent application Ser. No. 09/450,602 filed Nov.30, 1999.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to the field of encapsulatedcomponents and to the manufacturing of such components. This inventionrelates more specifically to the field of electrical components that areencapsulated to improve their resistance to vibration and corrosiveenvironments.

[0003] Encapsulation is a process by which a relatively fragilecomponent is surrounded by an encasing material which providesmechanical support to the component and which may seal the componentfrom contact with the ambient environment. Solid state electricaldevices are known to be susceptible to printed circuit board failuresdue to vibration loads and/or mechanical or electrical degradationcaused by exposure to a corrosive environment. The assignee of thepresent invention provides components for the marine environment whereinhigh levels of vibration and/or corrosive atmospheres may becommonplace. It is known to encapsulate such components to improve theirperformance in the marine environment. Encapsulants commonly used insuch applications include epoxy resin and urethane based products, andthey are selected for their workability, mechanical strength andelectrical insulating properties. As commonly practiced, the encapsulantis poured in a fluid state into a case containing electrical devices,then allowed to cure to form a solid mass encasing the electricaldevices within the case.

[0004] While the known process is effective to protect a componentagainst vibration and environmental damage, failures may occur withinthe component due to mechanical damage caused by the thermal growthcharacteristics of the encapsulant. For example, it is known that suchthermal growth may cause mechanical failure at the point where aconducting pin is soldered directly to a mating connector on a printedcircuit board when the pin is fully constrained by being molded into aplastic case. Encapsulant disposed between the printed circuit board andthe case is subject to thermal expansion and contraction. The thermalgrowth of the encapsulant may tend to move the printed circuit boardaway from the case. However, at the location of the soldered connection,the printed circuit board is maintained at a fixed distance from thecase. The thermal expansion of the encapsulant may impose unacceptablyhigh forces on the printed circuit board and/or the soldered connection.Encapsulated electrical components are known to have failed as theresult of such differential thermal expansion.

BRIEF SUMMARY OF THE INVENTION

[0005] Thus, there is a particular need for an improved method forencapsulating a component to avoid failures resulting from the thermalgrowth of the encapsulant. There is also a particular need for anencapsulated component having a greater resistance to thermal growthfailures.

[0006] Described herein is a method for encapsulating components withina case, the method comprising the steps of: forming a bladder having aninterior containing a collapsible insert; positioning the bladder withinthe case; installing at least one component within a case; depositing anencapsulant in a fluid state within the case and allowing theencapsulant to transform to a solid state; and providing a ventconnection to the bladder interior so that the collapsible insert maycompress and expand as the solid encapsulant expands and contracts. Aproduct formed by such a process is also described herein, as well as akit to be used for encapsulating a component by the described process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The features and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread with the accompanying drawings in which:

[0008]FIG. 1 is a partial sectional view of a printed circuit boardmounted within a case proximate an inflated bladder.

[0009]FIG. 2 is a partial sectional view of the apparatus of FIG. 1after being encased within an encapsulant.

[0010]FIG. 3 is a partial sectional view of the apparatus of FIG. 2wherein the bladder has been punctured by drilling a hole through thecase.

[0011]FIG. 4 is a top view of the bladder of FIGS. 1-3.

[0012]FIG. 5 is a partial sectional view of a printed circuit boardmounted within a case above a bladder containing a collapsible insertand having a chimney portion extending above the level of theencapsulant for venting the interior of the bladder.

[0013] Similar or identical components illustrated on successivedrawings are identified with the same numeral in each drawing.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The applicants have discovered a method and apparatus foraccommodating the thermal growth of an encapsulant disposed within acase. In the embodiment illustrated in FIGS. 1-3 an electrical printedcircuit board is encapsulated within a case. The apparatus 10 includes aprinted circuit board 12 housed within a case 14. As is known in theart, case 14 may be a one piece injection molded plastic component or ametal component, a partial bottom wall of which is illustrated inFIG. 1. A plurality of electrical devices 16 are mounted to printedcircuit board 12. The electrical devices 16 may constitute all or partof a circuit, such as for example, circuitry necessary to perform thefunction of a power supply. Electrical connection to the circuit board12 is provided by one or more conductive pins 18. The pins 18 may besealed within the wall of the case 14 as is known in the art ofinjection molding. Each pin is illustrated as being soldered to aconnector 20 mounted on circuit board 12, thereby providing bothmechanical and electrical connections between the case 14 and thecircuit board 12. Circuit board 12 may also be supported mechanically bypost 22 formed as an integral portion of the wall of case 14. A screw 24is shown attaching the circuit board 12 to post 22. The circuit board 12may also be secured directly to the case 14 by a screw or clamp, or maybe secured by the action of a connector attached to the case.

[0015] A bladder 26 is positioned within the case 14, and may beattached to a surface of the case by an adhesive 28. Bladder 26 is ahollow structure defined by a flexible wall member which takes apredetermined shape when inflated to an internal pressure that is higherthan the ambient external pressure. The bladder may be formed of aflexible, airtight material, such as polyvinylchloride (PVC). Othermaterials of construction for the bladder 26 may be selected for ease ofmanufacturing, electrical insulation properties, resistance to heat,and/or compatibility with the encapsulant material to be used. In theembodiment of FIG. 1, bladder 26 consists of two layers of PVC materialsealed on their respective edges 28 by a thermal sealing process.Bladder 26 is also illustrated as having a sealed hole 27 formed in onelocation for fitting around post 22. Such a hole 27 may be seen moreclearly in FIG. 4 which is a top view of bladder 26. FIG. 4 alsoillustrates the location of a section A-A which is the sectional view ofthe bladder 26 seen in FIGS. 1-3. Bladder 26 may be formed in anydesired shape, and it preferably will conform to the geometry of atleast a portion of the interior of case 14. The shape of bladder 26 isselected to match the shape of a desired space within case 14 devoid ofencapsulant, as will be described more fully below. The interior ofbladder 26 may be filled with air or other fluid so that the bladdertakes a predetermined shape when inflated. The bladder 26 may beinflated prior to being installed within the case 14, or for certainapplications, it may be installed in a deflated state and inflated onceit is in position within the case 14.

[0016]FIG. 2 illustrates the apparatus 10 of FIG. 1 after encapsulant 30has been deposited in the case 14. Prior to depositing the encapsulant30, the printed circuit board 12, electrical devices 16 and case 14 maybe preheated to a predetermined elevated temperature, such as about 85degrees Centigrade, for a period of time sufficient to remove moisturefrom the components including the printed circuit board 12. Encapsulant30 in a fluid state is then poured into the case 14 to a predeterminedlevel. In certain embodiments, it may be necessary to tilt the case 14and enclosed components while introducing the encapsulant 30 in order toavoid the entrapment of air under the circuit board 12, thereby ensuringthe complete encapsulation of all of the devices 16. In the embodimentof FIGS. 1-3, bladder 26 is positioned so that it does not contact anyportion of the printed circuit board 12. This insures that theencapsulant 30 will fully encase the electrical devices 16 located onthe side of the circuit board 12 proximate the bladder 26. Encapsulant30 is allowed to cure to transform to a solid state with the bladder 26in its inflated condition, thereby forming a space devoid of encapsulant30 at a desired location within the case 14.

[0017]FIG. 3 illustrates the apparatus 10 of FIGS. 1-2 with a hole 32having been drilled through case 14, thereby causing a puncture 34 inbladder 26. The puncture 34 allows the interior of bladder 26 to be influid communication with and at pressure equilibrium with the ambientenvironment of the apparatus 10. As encapsulant 30 grows due to anincrease in temperature, the space defined by the bladder 26 which isdevoid of encapsulant 30 may decrease to accommodate the thermalexpansion of the encapsulant 30. Without the puncture 34, thedeformation of encapsulant 30 and resulting decrease in volume of thespace devoid of encapsulant may result in an undesirable increase inpressure in bladder 26, thereby negating the desired affect of providingspace for the unimpeded thermal growth of encapsulant 30. Because theencapsulant 30 is free to grow into the space defined by bladder 26, thestresses generated in the printed circuit board and attached structuresare reduced. The material of bladder 26 is selected so that it remainsflexible during the operation of the apparatus 10 and so that it mayremain within the apparatus 10 throughout its operating life withoutdetrimental effect.

[0018] In lieu of drilling a hole 32 or otherwise penetrating the case14 in order to form puncture 34, the puncture 34 may be formed bycutting off a portion of bladder 6 extending above the top level ofencapsulant 30. Alternatively, a valve may be attached to the wall ofbladder 26 and made accessible outside the area of the encapsulant 30.Once the encapsulant 30 has transformed to a solid state, the valve maybe opened to provide a fluid communication path between the interior ofthe bladder 26 and the ambient environment.

[0019] The bladder 26 and encapsulant 30 may be supplied together with afully assembled apparatus 10, or they may be supplied separately as akit for installation subsequent to the assembly of the circuit board 12and case 14. Such a kit may include a bladder 26 shaped to fit withinthe case 14, along with a supply of encapsulant 30. The kit may alsoinclude a supply of adhesive 28, such as a tube of liquid adhesive, forsecuring the bladder 26 in its proper position while the encapsulant 30is poured into case 14.

[0020]FIG. 5 illustrates a cross-sectional view of an engine controller40 for a marine propulsion apparatus wherein a bladder 26 is formed tocontain a collapsible insert 36. Circuit board 12 supports andinterconnects a plurality of electrical devices 16 functional as part ofa control system for a marine engine (not shown). The type, quantity andinterconnection of such electrical devices 16 necessary to achieve suchfunctionality are well known in the art and may take any of manyembodiments. Bladder 26 is positioned within case 14 proximate thebottom 42 of the case 14 and may be affixed in its location by anadhesive 28. Bladder 26 is positioned between the circuit board 12 andthe case 14 to define a space devoid of encapsulant 30. In thisembodiment, there is no need to inflate bladder 26 since the collapsibleinsert 36 acts to maintain the bladder in an expanded condition duringthe pouring of the liquid encapsulant 30 into the case 14.

[0021] Flexible insert 36 may be a material having a resistance tocrushing sufficient to support bladder 26 in an expanded conditionduring the pouring of encapsulant 30 against the bladder 26, and acompressibility sufficient to allow for the expansion and contraction ofencapsulant 30 after it has hardened. In one embodiment, insert 36 is asection of 2-pound open cell polyester foam, such as is provided byFederal Foam Technologies, Inc. of New Richmond, Wis. The thickness ofthe insert 36 may be selected as a function of the expected expansionand contraction of the encapsulant 30 over the expected temperaturerange, and as a function of the allowable deflection in the circuitboard 12 that may be caused by such expansion and contraction. In oneembodiment a ¼ inch thick insert was used to create a space devoid ofencapsulant that otherwise would have been ¾ inch thick had it beencompletely filled with encapsulant.

[0022] Bladder 26 is formed to have an opening 44, and an end of insert36 may extend therefrom. Opening 44 functions as a vent to allow air toflow out of and into the bladder 26 as the encapsulant 30 expands andcontracts during temperature changes. The opening 44 may be formed to bepart of a chimney portion 46 of the bladder 26. The chimney portion 46extends upward away from the bottom 36 of case 14 from a bend 48 to thevent opening 44 located above a top level 50 of encapsulant 30. Opening44 may be formed in the bladder 26 during its original construction byremoving a sealed edge portion of the chimney 46 or by not sealing aportion of the perimeter of the bladder 26. It is important that thecollapsible insert be free to expand the bladder 26 to an expandedcondition prior to the step of pouring the liquid encapsulant 30 intothe case 14. One method of manufacturing the bladder 26 is to sandwich alayer of open foam material between two layers of PVC material and tosonically seal weld the edges of the PVC material together. The edges ofthe foam material are spaced away from the edges of the PVC material tobe welded in order to ensure that a good seal is created. The bladdermay be pressed flat during the welding process to improve the qualitycontrol of the welding process. Unless there is a path for air to enterthe bladder after the welding process, the two layers of PVC materialwill remain in a collapsed state. In this case, it is important for thevent opening 44 to be formed prior to the step of pouring the liquidencapsulant 30 into the case 14 in order to ensure that the collapsibleinsert 26 can expand the bladder 26. Preferably, insert 36 extendsthrough bend 48 to prevent the bladder sides from collapsing andcreating a seal preventing the flow of air into and out of the interiorof the bladder 26. This is particularly important when the bladder willbe exposed to an elevated temperature in order to remove moisture beforethe encapsulation process, since the elevated temperature may act tocause a welding of the opposed sides of the bladder within the bend 48.

[0023] It is possible to use the embodiment of FIG. 5 without a separatebladder material and with only the collapsible insert 36 defining thespace devoid of encapsulant. The selection of materials for such anapplication must consider any possible flow of the encapsulant 30 intothe collapsible insert 36 prior to the hardening of the encapsulant 30.For example, if an open cell foam material is used for the insert 36,the size and material of the cells and the viscosity of the liquidencapsulant will determine the rate of flow of the encapsulant into thecells. Any such migration of encapsulant prior to its solidificationwould, of course, decrease the compressibility of the insert 36 andshould be accounted for in the selection of the thickness of the insert.It is also possible to cover the insert 36 with a barrier material thatis impervious to the liquid encapsulant to prevent this undesirablemigration of encapsulant into the insert 26. Such barrier materials mayinclude, for example, a PVC plastic or a common kitchen cooking wrap.One or both sides of the insert 36 may need to be covered, dependingupon the specific application. Federal Foam Technologies, Inc. of NewRichmond, Wis. provides an open cell foam product laminated with aflexible polyester film that may be useful in such applications.

[0024] While the preferred embodiments of the present invention havebeen shown and described herein, such embodiments are provided by way ofexample only. Numerous variations, changes and substitutions will occurto those of skill in the art without departing from the inventionherein. For example, the embodiment illustrated in FIGS. 1-3 is for anelectrical printed circuit board component. Other embodiments mayinclude, for example, discreet electrical components, mechanicaldevices, sensors, or fragile containers, etc. mounted in a case.Accordingly, it is intended that the invention be limited only by thespirit and scope of the appended claims.

We claim as our invention:
 1. A method of encapsulating componentswithin a case, the method comprising the steps of: forming a bladderhaving an interior containing a collapsible insert; positioning thebladder within a case; installing at least one component within thecase; depositing an encapsulant in a fluid state within the case andallowing the encapsulant to transform to a solid state; and providing avent connection to the bladder interior so that the collapsible insertmay compress and expand as the solid encapsulant expands and contracts.2. The method of claim 1, wherein the step of positioning furthercomprises attaching the bladder to a surface of the case.
 3. The methodof claim 1, wherein the step of positioning further comprisespositioning the bladder not to contact any portion of the at least onecomponent.
 4. The method of claim 1, further comprising: attaching thebladder to a bottom surface of the case; mounting a circuit board in thecase above the bladder; and tilting the case while pouring theencapsulant into the case to ensure that the encapsulant flows betweenthe bladder and the circuit board.
 5. The method of claim 1, furthercomprising the steps of forming the bladder to have a predeterminedshape and positioning the bladder in a predetermined location within thecase so that a space devoid of encapsulant created by the bladder has apredetermined shape and location relative to the case and the at leastone component.
 6. The method of claim 1, further comprising the steps ofheating the at least one component, bladder and case to remove moistureprior to the step of depositing an encapsulant.
 7. The method of claim1, wherein the step of forming a bladder having an interior containing acollapsible insert comprises the steps of: providing an open cell foammaterial; providing a layer of plastic material on each of opposed sidesof the open cell foam material; and sealing respective mating edges ofthe plastic material around a perimeter of the open cell foam material.8. The method of claim 7, wherein the step of providing a ventconnection comprises removing a portion of the sealed mating edges.
 9. Aproduct formed by the process of: forming a bladder having an interiorcontaining a collapsible insert; positioning the bladder within a case;installing at least one component within the case; depositing anencapsulant in a fluid state within the case and allowing theencapsulant to transform to a solid state; and providing a ventconnection to the bladder interior so that the collapsible insert maycompress and expand as the solid encapsulant expands and contracts. 10.The product of claim 9, formed by the further step of attaching thebladder to a surface of the case.
 11. The product of claim 9, formed bythe further step of positioning the bladder not to contact any portionof the at least one component.
 12. The product of claim 9, formed by thefurther steps of: attaching the bladder to a bottom surface of the case;mounting a circuit board in the case above the bladder; tilting the casewhile pouring the encapsulant into the case to ensure that theencapsulant flows between the bladder and the circuit board.
 13. Theproduct of claim 9, formed by the further steps of forming the bladderto have a predetermined shape and positioning the bladder in apredetermined location within the case so that a space devoid ofencapsulant created by the bladder has a predetermined shape andlocation relative to the case and the at least one component.
 14. Theproduct of claim 9, formed by the further steps of heating the at leastone component, bladder and case to remove moisture prior to the step ofdepositing an encapsulant.
 15. The product of claim 9, wherein the stepof forming a bladder having an interior containing a collapsible insertcomprises the steps of: providing an open cell foam material; providinga layer of plastic material on each of opposed sides of the open cellfoam material; and sealing respective mating edges of the plasticmaterial around a perimeter of the open cell foam material.
 16. Theproduct of claim 15, formed by the further step of removing a portion ofthe sealed mating edges to provide a vent connection.
 17. An apparatuscomprising: a case; an electrical component disposed within the case;encapsulate disposed within the case and in contact with at least onesurface of the electrical component; a bladder disposed within the case;and a collapsible insert disposed within the bladder.
 18. The apparatusof claim 17, wherein the interior of the bladder is in fluidcommunication with the ambient environment of the apparatus.
 19. Theapparatus of claim 17, further comprising a puncture in the bladder. 20.The apparatus of claim 17, further comprising a hole in the caseproximate the puncture.
 21. The apparatus of claim 17, wherein thebladder comprises a PVC material.
 22. The apparatus of claim 17, whereinthe collapsible insert comprises an open cell foam material.
 23. A kitfor encapsulating a component within a case, the kit comprising: abladder shaped to fit within a case proximate a component; a collapsibleinsert disposed within the bladder; and encapsulant for at leastpartially filling the interior of the case to be in contact with thecomponent and the bladder.
 24. The kit of claim 23, wherein the bladdercomprises a PVC material.
 25. The kit of claim 23, wherein thecollapsible insert comprises an open cell foam material.
 26. The kit ofclaim 23, further comprising an adhesive for attaching the bladder to awall of the case.
 27. An apparatus comprising: a case; an electricalcomponent disposed within the case; encapsulate disposed within the caseand in contact with at least one surface of the electrical component; acollapsible insert defining a space devoid of encapsulant disposedbetween the electrical component and a portion of the case.
 28. Theapparatus of claim 27, wherein the collapsible insert comprises an opencell foam material.
 29. The apparatus of claim 28, further comprising alayer of material impervious to the encapsulant disposed between theencapsulant and the open cell foam material.
 30. The apparatus of claim27, wherein the collapsible insert comprises a bladder containing anopen cell foam material and having a vent connection.
 31. An apparatuscomprising: a case; an electrical component disposed within the case;encapsulate disposed within the case to a level covering the electricalcomponent; a bladder having a first portion disposed between a bottom ofthe case and the electrical component and having a chimney portionjoining the first portion at a bend and extending above the level of theencapsulant for venting an interior of the bladder; and an open cellfoam material disposed in the bladder.
 32. The apparatus of claim 31,wherein the open cell foam material extends from the first portionthrough the bend to the chimney portion.
 33. An engine controller for amarine propulsion apparatus comprising: a case; a circuit board attachedto the case at a predetermined height above a bottom of the case;encapsulate disposed within the case to a level covering the circuitboard; a bladder disposed between the bottom of the case and the circuitboard and defining a space devoid of encapsulant, the bladder containinga collapsible insert; the bladder further comprising a chimney portionextending above the level of the encapsulate to form a vent opening. 34.The engine controller of claim 33, wherein the collapsible insertcomprises an open cell foam material.
 35. The engine controller of claim34, further comprising: a bend formed in the bladder to define an end ofthe chimney portion; and the open cell foam material extending throughthe bend.
 36. A method of manufacturing an electrical component, themethod comprising the steps of: providing a case; positioning a bladdercontaining a collapsible insert proximate a bottom of the case, thebladder having a chimney portion extending upward away from the bottomof the case; mounting a circuit board within the case above the bladder,a top of the chimney portion extending above a top of the circuit board;filling the case with encapsulant to a level above the top of thecircuit board but below the top of the chimney portion, the bladderdefining a space devoid of encapsulant between the bottom of the caseand the circuit board.
 37. The method of claim 36, further comprisingthe step of removing a portion of the top of the chimney portion toprovide a vent connection to an interior of the bladder prior to thestep of filling the case with encapsulant.
 38. The method of claim 36,further comprising forming the bladder containing a collapsible insertby the steps of: providing an open cell foam material; covering the opencell foam material with a top layer of PVC material and a bottom layerof PVC material; sealing respective mating sides of the top layer andthe bottom layer of PVC material together around a perimeter of the opencell foam material.
 39. The method of claim 36, further comprising thesteps of: positioning the collapsible insert to extend into the chimneyportion; forming a bend in the bladder to extend the chimney portionupward away from the bottom of the case, the collapsible insertextending through the bend; heating the case, bladder and circuit boardto to remove moisture prior to the step of filling the case withencapsulant.
 40. A method of manufacturing an electrical apparatus, themethod comprising the steps of: providing a case; installing anelectrical component within the case; installing a collapsible insertbetween the case and the electrical component; introducing encapsulantinto the case to cover at least one surface of the electrical component,the collapsible insert defining a space devoid of encapsulant betweenthe case and the electrical component.
 41. The method of claim 40,further comprising forming the collapsible insert from an open cell foammaterial.
 42. The method of claim 41, further comprising the step ofcovering at least a portion of the open cell foam material with a layerof material impervious to the encapsulant prior to the step ofintroducing encapsulant.
 43. The method of claim 40, further comprisingthe steps of: forming a bladder around the collapsible insert prior tothe step of installing the collapsible insert.
 44. The method of claim43, further comprising the step of forming a vent opening in thebladder.
 45. The method of claim 44, further comprising the step offorming a bend in the bladder to position the vent opening above a toplevel of the encapsulant prior to the step of introducing encapsulant.